1. Field of the Invention
This invention relates to a method and system for wireless communication in fully distributed wireless networks. Particularly, it relates to a multihop routing method in a wireless communication network where each device or node is used as a packet carrier and forwarder and the packet is relayed to from the source to the destination hop by hop.
2. Description of the Related Art
Ultra-Wideband (UWB) technology is developed for bringing the convenience and mobility of wireless communications to high-speed interconnects in devices use in home and office environments. Designed for short-range, wireless personal area networks (WPANs), UWB is the technology for freeing people from wires, enabling wireless connection of multiple devices for transmission of video, audio and other high-bandwidth data. Based on short-range radio communication, UWB complements other longer range radio technologies such as Wi-Fi, WiMAX, and cellular wide area communications. It is used to relay data from a host device to other devices in the immediate area (up to 10 meters, or 30 feet).
While UWB is advantageous in terms of low power consumption, and high data rate, it also has the limitation of short transmission range (maximum 10 meters). This shortcoming cannot be overcome by simply increasing transmitting power because it would violates FCC regulations and shorten the device's battery life. Based on a new multi-hop routing method, one object of the present invention is to provide a solution to UWB's problems related to the short-range transmission.
Routing protocols in a device have been used to extend its communication coverage beyond its neighboring devices. The main task is to route information packets from the source device to the destination device which does not have a direct connection with the source device. In the wired network such as Internet where the network topology is quite stable, the routing protocol periodically updates the network topology information so that the path to every destination is known before routing the packet. Those routing protocols are categorized as proactive routing protocol.
However, in wireless networks such as those based on the UWB technology, the topology can change quite rapidly. The devices in the wireless network are movable and the channel conditions are changing. The topology information at a time may not be valid after a period of time. For these reasons, reactive routing protocol, instead of proactive routing protocol, was proposed for wireless networks. Reactive routing protocol does not maintain the network topology information.
Bandwidth Reservation along a path was first proposed in Resource Reservation Setup Protocol (RSVP) for wired networks. It reserves the path from a device to a device, starting from the destination. As it is used in wired network, the whole network topology is known in advance. Hence, each routing device could be able to direct the bandwidth reservation request to the source very efficiently. However, such method of bandwidth reservation has difficulties when used in wireless networks. First, the network topology information that each device maintains is very limited. Second, there is the hidden node problem where the bandwidth reservation with two parties may affect the bandwidth utilization of the neighbors around the parties. This makes the reservations among the devices inter-dependent. Third, the channel quality is unstable in a wireless network. Some QoS performance may be required to maintain in order to have a stable path.
To deal with the hidden node problem in wireless network, Lin, et al. proposed a method that can avoid the hidden node problem and at the same time also optimize the bandwidth utilization (Lin C. R. et al., QoS Routing in ad Hoc Wireless Networks, IEEE Journal on Selected Areas in Comm., August 1999). However, it requires that the route discovery stage be finished before the bandwidth reservation starts. This introduces two problems: slow response time and low successful rate. This is mainly because the method separates the bandwidth reservation stage from the route discovery stage.
To deal with the limited network topology problems and improve the response time and successful rate, it has been suggested to combine the bandwidth reservation stage with the route discovery stage and to support multipath reservation. It has been further suggested to introduce an additional status for the slots that bandwidth reserved to deal with the potential hidden node problem (a slot is used in TDMA system as a unit of bandwidth). By doing so, the successful rate and response time are improved. However, the amount of redundant bandwidth reservation is increased significantly and likely to offset the improvement made on the successful rate. Therefore, modifications on the routing method are needed to overcome the problems encountered in the art.